The Trump administration Tuesday tightened its web of sanctions around the Maduro regime in Venezuela, blacklisting four companies allegedly involved in the country’s oil sector. By sanctioning the firms and their vessels, which are registered in the Marshall Islands and Greece, the U.S. Treasury Department is attempting to cut off the flow of revenue President Nicolás Maduro needs to preserve his power. Targeting the private sector with financial sanctions also helps the administration avoid a military confrontation,…